Multiple-line key telephones, sometimes referred to as "trader turrets", have been widely used during the past decade in rapid communications networks such as trading operations in banks, brokerage houses, and other financial institutions. Telephones of this type provide direct access to several hundred outside lines with the simple depression of a single key on the telephone. Connections to the outside world may be established without dialing. Each telephone unit, also referred to as a telephone station, may be capable of selecting any one of several hundred different lines, and should at the same time provide all normal telephone functions, e.g., dialing, ringing, hold, etc.
Another important feature of multiple-line telephones is the provision in each telephone station for indicating the present status of each of the lines accessible at the particular station. This indication usually takes the form of a continuously lighted key for a "busy" line, a flashing key for a line on "hold" or for a "ring" on an incoming call, and a non-lighted key for a free line. In addition, the station should have the capability of indicating which line the user has picked up. The use of non-locking pushbutton keys requires some type of visual indication to allow the user to have information on all lines, particularly the line to which he is connected. An earlier turret system using non-locking pushbuttons is described in U.S. Pat. No. Re. 31,144 for "Multi-Station Telephone Switching System".
With considerable advances in technology the number of lines available to any one operator has increased tremendously. In order to fit all these keys in a system one solution is the use of a paging module where the operator can page through various selectable lines on the main or control station until the desired page is displayed. The operator can then press the corresponding button to establish a connection. This pagination feature allows the user to select and display different groups of line assignments known as "pages" from a pool of available numbers. The paging module usually has an electro-luminescent display similar to a display on a computer terminal. The module can display all the available lines in the system in a specific number of groups of lines. Each group of lines is called a page. The non-locking keys are aligned on the display such that there is a descriptor for each corresponding key. The descriptors that identify each line automatically change when a new page is selected.
With the pagination feature, the module allows the trader to have access to a great number of lines while taking up only a small amount of desk space. The trader can also conveniently operate with one module.
However, a problem encountered with the paging feature is that the operator is unable to view the status of a large number of lines at the same time. One possible way to solve this problem is constructing additional modules with all the lines and corresponding keys in place. The operator will then have a view of all the possible lines and their status. The operator can select a line by depressing the corresponding key on one of the additional modules. This solution, however, requires a considerable amount of space due to the large number of physical keys or buttons. Every station, therefore, will become very large, something which is not desirable in a trading floor or any other telephone communications application.